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Methods Fail: Testing the pre-menopausal cougar hypothesis.

ScienceDaily has an article from earlier this month, Ticking Biological Clock Increases Women's Libido, New Research Shows, that claims that women who are approaching menopause become "more willing to engage in a variety of sexual activities to capitalize on their remaining childbearing years" and that they are more prone to one night stands and "adventurous bedroom behavior" than their younger counterparts. According to the article:

Compared with the other groups, women with low fertility were more likely to experience:- Frequent sexual fantasies- Thoughts about sexual activities- More intense sexual fantasies than their younger counterparts- A more active sex life and willingness to have a one-night stand- A willingness to have casual sex

Bear in mind that this 'low fertility group', as they have chosen to define it, stretches all the way from 27-45 year old women. I am only one year away from this group, and already my sex drive is much lower than it was in my teens and early twenties, so this does not jibe at all with my own experiences, but, hey, whatever. Everyone's different, and it is hard to deny the cougar phenomenon, as much as I hate that word. However I find it hard to believe that women age 27-35 or so could possibly be considered to have 'low fertility'. To get to the bottom of this rationale, and also to determine how the authors defined such things as "casual sex" and "more intense sexual fantasies" I looked up the source paper: Reproduction expediting: Sexual motivations, fantasies, and the ticking biological clock by Easton et al.

After reading the article it seems that women experience a drop in fertility from their late 20s to mid 30s, which rapidly drops off after 35. Okay, so they're lower fertility, perhaps, but I still think it is a stretch to say that they have low fertility. Whatever. Now on to the terminology of "intense sexual fantasies":

The intensity of a sexual fantasy also influences motivation to engage in sexual activity such that more intense sexual fantasies are correlated with higher rates of sexual intercourse (e.g., Rösler & Witztum, 1998). RE women should therefore experience more intense sexual fantasies than women who are not expediting reproduction (Prediction 1.3). Previous research on differences in sexual fantasies as a function of age indicated women between the ages of 26 and 35 reported more sexual fantasies than younger and older women (e.g., Purifoy et al., 1992), lending partial support to the present predictions.

Do you see in there, anywhere, a way of measuring the relative 'intensity' of a sexual fantasy? Yeah, me either. On to the methods (where I found out that the participants were self-selected from Craigslist, which I'll get to in a minute):

Participants answered several questions regarding their sexual thoughts, fantasies, and behaviors. Using 1–7 Likert scales, participants answered how often they think about sexual activities (never to over 10 times a day), how frequently they fantasize about sex (never to daily) and how intense their fantasies are (very mild to very intense). Lower scores indicated less time, frequency, or lower intensities.

Still no definition of 'intensity' for sexual fantasies. If the women are asked to determine for themselves what constitutes a mild vs. intense sexual fantasy, there is going to be extreme variation between individuals based on their sexual experiences, what is considered 'normal' sex based on their exposure and values, and all types of demographic factors (age, sexuality, location, etc). This is a very amorphous interpretation of the idea at best. Also... let's be real. Craigslist attracts a certain kind of people. I'm not making a judgment on the people who use Craigslist, I'm just saying it's a niche market with a very large personals section. These are confounding factors that I think bias the study in ways the authors didn't discuss.

Another thing about Craigslist (and this is just my very subjective opinion based on my own experiences): it is widely used by younger people (in the 20s demographic) because it is generally younger people who are looking for jobs, apartments, and using the personal ads to find romantic partners (this is backed up by the sample sizes of their volunteers, as about 600 were between the ages of 18-26 and only about 200 were between the ages of 27-45). People who are a bit older are generally more settled in their lives, they already have homes and jobs and are more likely to have long term partners. I would say that people who are in their mid-30s who are using Craigslist have probably recently experienced an upset in the flow of their life: the loss of a job or a partner, or recent relocation due to the loss of a job or partner. These things might cause a person to be more sexually adventurous because they either need to find a new partner OR they need something to keep them sane while they try to get their life back on track (whether they're having that extra sex with their partner or with others). What this boils down to is that I would say that the 20s demographic of Craigslist users probably are a relatively decent representation of 20s in the population, whereas Craigslist users in their 30s and 40s probably represent a much smaller subset of the population, likely either a disrupted and/or 'hornier' population. Again, these are just my opinions based on my experience with Craigslist and the people who use it.

As an interesting aside, in the results section, the authors note that people who reported anything other than a heterosexual orientation were excluded from the analysis. Why? What is the rationale for this? That's a question I would dearly like to see answered.

I am glad that the authors acknowledge that their results may not be based on fertility at all:

The present findings may reflect mere sexual experience increasing comfort with sexuality, and not by a reproduction expediting adaptation designed to capitalize on remaining fertility. Differences in sexual experience would explain why younger women were consistently different from older women. Previous research indicates sexual fantasy behavior changes as a function of sexual experience. Women with more sexual experience report having more sexual fantasies than those with less sexual experience (e.g., Pelletier & Herold, 1988).

I don't think that the rationale for this paper is inherently flawed, but I do think that the methods used to test their hypothesis could have been way, way better. My main issue is their choice to use self-selected volunteers from Craigslist as their sample population. I also take issue with their lack of hard definitions for the intensity of sexual fantasies, which vary wildly across populations and between individuals.

7 comments:

This one is incredibly easy. Women age 27-45 with low fertility have zero children. Women in the same age with medium high fertility (=me) have children; sometimes several, often young. I sure feel way more sexy in the (rare) occasions when my kids aren't in the next bedroom, not to mention how totally unsexy I felt when I was nursing twins! Every time I saw a bed I looked at it with the intense desire to... sleep. This paper belongs in the IgNobel prize list.

I honestly cannot believe that they sampled from craigslist. There's reason to suspect (and, as far as I know, no good evidence to the contrary) that people who use craigslist personals are atypical of the general population. In larger, more general surveys that take pains to reach a cross-section of society sampling bias is still a problem. How did the authors expect it not to be a problem in a small survey that samples a self-selected subset of a self-selected subset of internet users?

That’s quite surprising, and looks fairly strongly like a methods FAIL. It seems odd to me that they’ve mentioned potential alternative interpretaitions, but not any potential lack of generalisability to the wider population. Would that have been seen as a more serious flaw by reviewers?

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I'm Michelle, a newly minted M.Sc. from an ecophysiology lab, and a technical editor for a scientific journal publishing group. Physiologically, I have an overactive sympathetic nervous system. Personally, I am agoraphobic and kind of a nerd. In my free time I blog and drink way too much tea.